Screw fasteners and terminal boards incorporating the same



March 10, 1964 OESTEREICHER 3,124,408

' SCREW FASTENERS AND TERMINAL BOARDS INCORPORATING THE SAME Filed Feb. 15. 1962 2 Sheets-Sheet 1 53 INVENTOR.

LOUIS 0E3 TEREI CHER BY v G I 6% 4 m gflivz ATTYS.

United States Patent corporation of New York Filed Feb. 13, 1962, Ser. No. 173,094 9 Claims. (Cl. 339-220) The present invention relates to screw fasteners and to terminal boards incorporating the same.

It is a general object of the present invention to provide a screw fastener of improved construction and arrangement, so that the screw fastener is of the self-threading type and so that after initial forward driving of the screw fastener into a set position with respect to an associated workpiece, ready retrograde movement of the screw fastener is automatically limited to a partially withdrawn position with respect to the workpiece.

Another object of the invention is to provide a screw fastener of the type described, wherein the ready movements of the screw fastener between its set and partially withdrawn positions with respect to the associated workpiece are established by two separate threads carried by the shank of the screw fastener and their respective cooperations with threaded structure formed in the workpiece in the initial forward driving of the screw fastener into its set position with respect to the workpiece.

A further object of the invention is to provide the combination of a terminal strip and a screw fastener of the type described, whereby the screw fastener serves as a terminal screw in the combination and may be readily operated as required between its set and partially Withdrawn positions for the purpose of selectively making secure external electrical connections with respect to the terminal strip.

A still further object of the invention is to provide the assembled combination of a terminal board formed of electrical insulating material, a terminal element carried by the terminal board and a screw fastener of the type described carried by the terminal element and serving as a terminal screw for the terminal element, wherein the terminal screw may be readily operated as required between its set and partially withdrawn positions, without the possibility of excessive retrograde movement of the terminal screw and the consequent loss thereof from its assembled position with respect to the terminal element.

Further features of the invention pertain to the particular arrangement of the elements of the screw fastener and of the elements of the assembly of the terminal board and the terminal element and the screw fastener as the terminal screw for the terminal element; whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a screw fastener embodying the present invention;

FIGURE 2 is a reduced front elevational view of a terminal element carried by the illustrated fragmentary portion of a terminal board, which terminal element is adapted to carry, as a terminal screw therefor, the screw fastener of FIG. 1;

FIG. 3 is a reduced rear elevational view of the terminal element and the associated fragmentary portion of the terminal board, as shown in FIG. 2;

FIG. 4 is a reduced vertical sectional view of the terminal element and the associated fragmentary portion of the terminal board, as shown in FIGS. 2 and 3, this view being taken in the direction of the arrows along the line 4-4 in FIG. 2;

FIG. 5 is an elarged fragmentary vertical sectional view of the workpiece and the front portion of the shank of the screw fastener, illustrating the initial threaded structure that is formed in the workpiece by the action of the front thread that is carried by the front portion of the shank of the screw fastener of FIG. 1; and

FIG. 6 is a fragmentary vertical sectional view, similar to FIG. 5 of the workpiece and the rear portion of the shank of the screw fastener, illustrating the final threaded structure that is formed in the workpiece by the combined actions of the front thread and the rear thread respectively carried by the front portion and the rear portion of the shank of the screw fastener of FIG. 1.

Referring now to FIG. 1 of the drawings, there is illustrated a scr w fastener lll embodying an elongated shank 11 and an enlarged head 12 of any suitable type terminating the rear end of the shank ll. More particularly, the screw fastener ltl is of the self-threading or self-tapping type and is especially adapted for use as the terminal screw in combination with an associated therminal element, as explained more fully hereinafter; whereby the head 12 comprises a binding head that is provided with the usual annular wire-receiving recess 12a disposed in the work-engaging face thereof and in surrounding relation with respect to the rear end of the shank 11. Also, the outer end of the head 12 carries a conventional slot 1211 that is adapted to receive the outer end of a screwdriver or other driving tool, in the usual manner.

A first rolled thread 20 is carried by the front portion 11a of the shank 11 and includes a number of helical turns and having a first fixed pitch; and a second rolled thread 30 is carried by the rear portion 11b of the shank 11 and includes a number of helical turns and having a second fixed pitch. The frontmost turn of the first thread 20 terminates adjacent to the front end of the shank 11 and the rearmost turn of the second thread 3t) terminates adjacent to the rear end of the shank 11, while the rearmost turn of the first thread Zll and the frontmost turn of the second thread 30 both terminate adjacent to the boundary between the front and rear portions Ma and 11b of the shank 11 and closely adjacent to and in alignment with each other so that the first and second threads 20 and 3d constitute continuations of each other along the shank 11. As illustrated, the sum of the lengths of the threads 2% and 3t along the shank 11 is equal to L1, the first thread 26 has a length along the shank ll. of L2, and the second thread 33 has a length along the shank 11 of L3.

As a constructional example of the screw it the shank 11 may have a No. 6 diameter, whereby the two threads Zll and 30 have substantially the same major diameter D1 and have substantially the same minor diameter D2. The first thread 20 has a relatively coarse pitch corresponding to twenty-four threads per inch of the front portion 11a of the shank ll; while the second thread 3% has a relatively fine pitch corresponding to thirty-two threads per inch of the rear portion 11b of the shank ii.

The extreme front end of the shank 11 is provided with a pilot end portion, indicated at 11c that has a diameter somewhat smaller than the minor diameter D2 of the first thread 20 so as to facilitate insertion thereof into the pilot hole provided in the associated workpiece. The leading portion 21a of the frontmost turn 21 of the first thread 20 has a crest diameter that is smaller than the major diameter D1 of the first thread 20; the trailing portion 22a of the rearmost turn 22 of the first thread 20 has a crest diameter that is smaller than the major diameter D1 of the first thread 26; and the leading portion 31a of the frontmost thread 31 of the second thread 30 has a crest diameter that is smaller than the major diameter D1 of the second thread 31). Accordingly, the front end of the first thread 29 is forwardly and inwardly tapered, as indicated by the broken line 21x; the rear end of the first thread 2i is rearwardly and inwardly tapered, as indicated by the broken line 21y; and the front end of the second thread 30 is forwardly and inwardly tapered, as indicated by the broken line 31x. In the first thread 2d, the crests of the turns have a substantially V-shape; while in the second thread 3%, the crests of the turns have a small amount of truncation. Also, in the first thread 26, the roots of the turns have a great amount of truncation; while in the second thread 36, the roots of the turns have a small amount of truncation.

As illustrated in FIG. 1, the screw should be utilized in a workpiece, indicated at 40 that has a thickness T that is somewhat less than the length L3 of the second thread 30 so that the front end of the second thread Tall projects entirely through the threaded structure provided in the workpiece 4-9 when the screw it) occupies its set position. In the arrangement illustrated, the front end of the second thread 30 projects by the distance L4 through the workpiece 4% whereby the length L3 of the second thread 3i? along the shank 11 of the screw it is equal to the thickness T of the workpiece 49 plus the distance L4.

The screw It) may be formed, for example, of steel, and involving a rolling step and utilizing a forged blank. Initially the blank mentioned comprises the upset head 12 and the adjacent shank 11 formed integrally therewith, the shank 11 including the substantially cylindrical body portion and the forwardly tapered front end portion. The blank mentioned is subjected to the rolling step noted, involving rolling dies, whereby simultaneously the first thread is formed upon the front portion 11a of the shank l1 and the second thread 3th is formed upon the rear portion lllb of the shank 11, as previously described in conjunction with FIG. 1. More particularly, the configuration of the threads 20 and are completely defined in the single rolling step mentioned; and thereafter, the screw 16 is subjected to a heat-hardening step in order to effect corresponding hardening of the threads 20 and 30, in the usual manner. Ultimately, the screw 10 may be provided with a finished coating of cadmium, or the like, in a conventional manner.

Considering now the mode of operation and the utilization of the screw N, and referring to FIGS. 5 and 6-, a substantially cylindrical pilot hole 40a is initially provided through the workpiece 48 that may be formed of a metal, such as brass, mild steel, etc. In the initial driving of the screw Til, the forwardly tapered pilot end 110 of the shank 11 is inserted into the front side of the pilot hole ida. The screw 10 is pressed home and rotated, in the usual manner, whereby in the initial driving thereof, the first thread 20 provided upon the front portion 11a of the shank 11 forms a corresponding first threaded structure 41 interiorly of the pilot hole 49a in the workpiece; the first threaded structure 4-1 comprises an internal thread having a pitch of corresponding to that of the first thread 2%, as shown in FIG. 5. Upon further rotation of the screw it the first thread 2% moves forwardly out of the first threaded structure 41 provided interioriy of the pilot hole 49a in the workpiece 40 and the second thread 39 moves forwardly into the first threaded structure ii mentioned. As the screw lit is driven further forwardly into its set position with respect to the workpiece 465, as shown in FIG. 6, the second thread 313 breaksup the first threaded structure 41 mentioned and forms a corresponding second threaded structure interiorly of the pilot hole 40a in the workpiece 46'; which second threaded structure 42 comprises an internal thread having a pitch of corresponding to that of the second thread 35 Thus, it will be understood that the formation of the second threaded structure 42 in the workpiece 46 by the second thread 3% carried upon the rear portion 11b of the shank 11 mutilates the first threaded structure 41 that was initially formed in the workpiece 40 by the first thread 20 carried by the front portion 11a of the shank 11.

Considering now the initial retrograde movement of the screw 10 from its-set position, as shown in FIG. 6, back into a partially withdrawn position with respect to the workpiece 40, the second thread 30 rotates readily in the second threaded structure 42 provided in the workpiece 46 and until the rear end of the first thread 2% is drawn into the threaded structure 42. At this time, and in further retrograde movement of the screw ill) beyond its partially withdrawn position with respect to the workpiece 44 the first thread 20 binds in the structure 42, thereby effectively to secure the screw 10 to the workpiece 40 and to establish the previously described limited range of subsequent ready movements of the screw 10 between its set position, as shown in FIG. 6, and its partially withdrawn position, as described above. It will be appreciated that the limited range of subsequent ready movements of the screw 10 between its set position and its partially withdrawn position with respect to the workpiece 4-0 is established primarily by the distance L4 and corresponding to the forward projection of the front end of the second thread 30 inwardly beyond the rear side of the workpiece 4%, as best shown in FIG. 1.

Of course, it will be appreciated that by forcing the screw 10, further retrograde movement beyond its partially withdrawn position described above, may be efected, but in this further retrograde movement, the turning of the screw 10 is difficult, since the first thread 20 must break-up the second threaded structure 42 in the workpiece 40 and re-form the first threaded structure 41 therein, in a reverse sequence with respect to that which occurred in the initial driving of the screw 10 into its set position with respect to the workpiece 40, in the manner previously described.

The screw fastener 10. is admirably suited for use as the terminal screw for a terminal element carried by a terminal board, which combination is illustrated in FIGS. 2 to 4, inclusive. More particularly, the terminal board 50 comprises a sheet of electrical insulating material and may be formed of a suitable phenol-formaldehyde resin. Two adjacent holes 51 and 52 are provided through the terminal board 5%) and a counter recess 53 is provided in the rear side of the terminal board 50 in surrounding relation with respect to the hole 52 therethrough so as to provide an internal ledge 54 in surrounding relation With respect to the hole 52, as clearly illustrated in FIG. 4.

Also, the combination comprises a terminal element 69 that includes a rearwardly projecting terminal clip 61 and an adjacent rearwardly projecting substantially cylindrical barrel 62. The terminal element 60 is assembled on the front side of the terminal board 50 with the terminal clip 61 projecting through the hole 51 and with the substantially cylindrical barrel 62 projecting through the hole 52. At this time, a suitable clamping tool is utilized to upset the extreme inner end of the barrel 62, so as to provide a surrounding annular flange 62a thereon in engagement with the adjacent surface of the ledge 54; whereby the barrel 62 frictionally secures the terminal element 60 in place upon the front side of the terminal board 50, in the general manner of an eyelet. Further, the front side of the terminal element 6% comprises a pair of upstanding and forwardly projecting ears 63, as shown in FIGS. 2 and 4, that are utilized for the conventional purpose of limiting movement of an external electrical connection that is made to the terminal element 60.

After the terminal element 69 has been secured to the terminal board 59 in a conventional manner, as described above, there results a substantially cylindrical pilot hoie 62b extending through the substantially cylindrical barrel 62; and into the pilot hole 62b, the screw fastener, indicated at N in FIG. 4, is driven in the manner pre- ,viously described; whereby the substantially cylindrical barrel 62 comprises the workpiece into which the screw is initially driven into its set position, in the manner previously explained.

In the terminal board combination of FIGS. 2 to 4, inclusive, the permanent electrical connection is made to the terminal clip 61 and the removable electrical connection is selectively made to the frontside of the element 60, utilizing the screw fastener 16* as the terminal screw. Also, it is mentioned that it is conventional to provide a coating of tin upon the terminal element 6!) truncation and the roots of the turns of said second thread in order to facilitate the electrical connections mentioned I and particularly to facilitate soldering of the permanent electrical connection to the terminal clip 61.

In this terminal board combination, the terminal screw 110 may be readily operated as required between its set position and its partially withdrawn position with respect to the barrel 562 for the purpose of selectively connecting and disconnecting the removable electrical connection or terminal with respect to the terminal element 6%; which operations of the .terminal screw it) do not mutilate the second threaded structure mentioned that is formed internally of the pilot hole 6217 provided in the barrel 62, as previously explained. However, in the event of further retrograde movement of the terrnial screw it beyond its partially withdrawn position, the first thread 26 provided on the front portion lllla of the shank it binds in the second threaded structure mentioned that is formed in the pilot hole 6% provided in the barrel 62, thereby to limit further retrograde movement of the terminal screw 1 beyond its partially withdrawn position mentioned. This arrangement positively secured the terminal .screw it? to the terminal element 69 so as to prevent loss thereof from the assembled combination nothwithstanding repeated operations of the terminal screw between its set and partially withdrawn positions in selectively securing and removing external, electrical connections with respect to the terminal element 6% In view of the foregoing, it is apparent that there has been provided a screw fastener of improved construction and arrangement so that the screw fasteneris of the selfthreading type and so that after initial forward driving of the screw fastener into a set position with respect to an associated workpiece, ready retrograde movement of the screw fastener is limited to a partially withdrawn position with respect to the workpiece. Also, there has been provided the combination ofa terminal board, a terminal element carried by the terminal board, and a terminal screw carried by the terminal element, wherein the terminal screw is of the construction and arrangement described, so that after initial driving of the terminal screw with respect to the terminal element, the same is securely electrical connections to the terminal element.

While there has been described what is at present considered to be the preferred embodiment of the invention,

it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A screw fastener of the self-threading type comprising an elongated shank, an enlarged head terminating the rear end of said shank, a first thread carried by the front portion of said shank and including a number of helical turns and having a first fixed pitch, and a second thread carried by the rear portion of said shank and including a number of helical turns and having a second fixed pitch, the frontmost turn of said first thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread having a small amount of truncation, whereby in the forward driving movement of said fastener into a set position with respect to an associated workpiece said first thread forms a corresponding first threaded structure in the workpiece pilot hole and then said second thread breaks-up the first threaded structure mentioned and forms a corresponding second threaded structure in the workpiece pilot hole, and whereby in initial retrograde movement ,ofsaidfastener from its set position into a partially withdrawn position with respect to the workpiece said second thread rotates readily in the second threaded structure mentioned and in further retrograde movement of said fastener beyond its partially withdrawn position with respect to the workpiece said first .thread binds in the second threaded structure mentioned, thereby effectively to secure said fastener to the workpiece and to establish a limited range of subsequent ready movements of said fastener between its set position and its partially withdrawn position.

2. A screw fastener of the self-threading type comprising an elongated shank, an enlarged head terminating the rear end of said shank, a first thread carried by the front portion of said shank and including a number of helical turns and having a first fixed pitch, and a second thread carried by, the rear portion of said shank and including a number of helical turns and having a second fixed pitch, the frontmost turn of said first thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread and the frontmost turn of said secondthread both terminating adjacent to the boundary between the front and rear portions of said shank and closely adjacent to and in alignment with each other so that said first and second threads constitute continuations of each other along said shank, said first and second threads having substantially the same major diameter and having substantially the same minor diameter and said first pitch being largerthan said second pitch, whereby in the forward driving movement of said fastener into a set position with respect to an associated workpiece said first thread forms a corresponding coarse threaded structure in the workpiece pilot hole and then said second thread breaks-up the coarse threaded structure mentioned and forms a corresponding fine threaded structure in the workpiece pilot hole, and whereby in initial retrograde movement of said fastener from its set position into a partially withdrawn position with respect to the workpiece said second thread rotates readily in the fine threaded structure mentioned and in further retrograde movement of said fastener beyond its partially withdrawn position with respect to the workpiece said first thread binds in the fine threaded structure mentioned, thereby effectively to secure said fastener to the workpiece and to establish a limited range of subsequent ready movements of said fastener between its set position and its partially withdrawn position.

3. A screw fastener of the self-threading type comprising an elongated shank, an enlarged head terminating the rear end of said shank, a first rolled thread carried by the front portion of said shank and including a num ber of helical turns and having a first fixed pitch, and a second rolled thread carried by the rear portion of said shank and including a number of helical turns and having snaanos a a second fixed pitch, the frontmost turn of said shank thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread and the frontmost turn of said second thread both terminating adjacent to the boundary between the front and rear portions of said shank and closely adjacent to and in alignment with each other so that said first and second threads constitute continuations of each other along said shank, said first and second threads having substantially the same major diameter and having substantially the same minor diameter and said first pitch being larger than said second pitch, whereby in the forward driving movement of said fastener into a set position with respect to an associated workpiece said first thread forms a corresponding coarse threaded structure in the workpiece pilot hole and then said second thread breaks-up the coarse threaded structure mentioned and forms a corresponding fine threaded structure in the workpiece pilot hole, and whereby in initial retrograde movement of said fastener from its set position into a partially withdrawn position with respect to the workpiece said second thread rotates readily in the fine threaded structure mentioned and in further retrograde movement of said fastener beyond its partially withdrawn position with respect to the workpiece said first thread binds in the fine threaded structure mentioned, thereby effectively to secure said fastener to the workpiece and to establish a limited range of subsequent ready movements of said fastener between its set position and its partially withdrawn position.

4. The screw fastener set forth in claim 2, wherein the leading portion of the frontmost turn of said first thread has a crest diameter that is smaller than the major diameter of said first thread, the trailing portion of the rearmost turn of said first thread has a crest diameter that is smaller than the major diameter of said first thread, and the leading portion of the frontmost turn of said second thread has a crest diameter that is smaller than the major diameter of said second thread.

5. The screw fastener set forth in claim 2, wherein the turns of said first thread have substantially V-shaped crests, and the turns of said second thread have truncated crests.

6. The screw fastener set forth in claim 2, wherein the terminal end of the rearmost turn of said first thread and the terminal end of the frontmost turn of said second thread merge into each other at the boundary between the front and rear portions of said shank.

7. In combination: a workpiece having a given thickness and provided with a threaded opening therethrough; and a screw fastener secured in place said threaded opening and readily movable with respect to said workpiece between a set position and a partially withdrawn position, said fastener being of the self-threading type and comprising an elongated shank, a first thread carried by the front portion of said shank and including a number of helical turns and having a first fixed pitch, and a second thread carried by the rear portion of said shank and including a number of helical turns and having a second fixed pitch, the frontmost turn of said first thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread and the frontmost turn of said second thread both terminating adjacent to the boundary between the front and rear portions of said shank and closely adjacent to and in alignment with each other so that said first and second threads constitute continuations of each other along said shank, said first and second threads having substantially the same major diameter and corresponding to that of said threaded opening, said first and second threads having substantially the same minor diameter and corresponding to that of said threaded opening, said first and second pitches being substantially different from each other and said second pitch corresponding to that of said threaded opening, said second thread having a length along said shank that is somewhat greater than the thickness of said workpiece and being arranged in engagement with said threaded opening, whereby in the initial forward driving movement of said fastener into its set position with respect to said workpiece said first thread forms a corresponding threaded structure in a pilot hole provided in said workpiece and then said second thread breaks-up the threaded structure mentioned and forms the structure of said threaded opening, and whereby in initial retrograde movement of said fastener from its set position into its partially withdrawn position said second thread rotates easily in said threaded opening and in further retrograde movement of said fastener beyond its partially withdrawn position said first thread binds in said threaded opening, thereby effectively to secure said fastener in place in said threaded opening and to establish said ready movements of said fastener between its set position and its partially withdrawn position.

8. In combination, a terminal strip having a given thickness and provided with a threaded opening therethrough; and a terminal screw secured in place in said threaded opening and readily movable with respect to said terminal strip between a set position and a partially withdrawn position, said terminal screw being of the selfthreading type and comprising an elongated shank, a first thread carried by the front portion of said shank and including a number of helical turns and having a first fixed pitch, and a second thread carried by the rear portion of said shank and including a number of helical turns and having a second fixed pitch, the frontmost turn of said first thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread and the frontmost turn of said second thread both terminating adjacent to the boundary between the front and rear portions of said shank and closely adjacent to and in alignment with each other so that said first and second threads constitute continuations of each other along said shank, said first and second threads having substantially the same major diameter and corresponding to that of said threaded opening, said first and second threads having substantially the same minor diameter and corresponding to that of said threaded opening, said first and second pitches being substantially different from each other and said second pitch corresponding to that of said threaded opening, said second thread having a length along said shank that is somewhat greater than the thickness of said terminal strip and being arranged in engagement with said threaded opening, whereby in the initial forward driving movement of said terminal screw into its set position with respect to said terminal strip said first thread forms a corresponding threaded structure in a pilot hole provided in said terminal strip and then said second thread breaks-up the threaded structure mentioned and forms the structure of said threaded opening, and whereby in initial retrograde movement of said fastener from its set position into its partially withdrawn position said second thread rotates easily in said threaded opening and in further retrograde movement of said fastener beyond its partially withdrawn position said first thread binds in said threaded opening, thereby effectively to secure said fastener in place in said threaded opening and to establish said ready movements of said fastener between its set position and its partially withdrawn position.

9. in combination: a terminal board formed of electrical insulating material and having a hole formed therethrough; a terminal element carried by said board and including a body arranged in said hole and frictionally secured in place therein, said body having a given length and provided with a threaded opening therethrough; and a terminal screw secured in place in said threaded opening and readily movable with respect to said body between a set position and a partially withdrawn position,

said terminal screw being of the self-threading type and comprising an elongated shank, a first thread carried by the front portion of said shank and including a number of helical turns and having a first fixed pitch, and a second thread carried by the rear portion of said shank and including a number of helical turns and having a second fixed pitch, the frontmost turn of said first thread terminating adjacent to the front end of said shank and the rearmost turn of said second thread terminating adjacent to the rear end of said shank, the rearmost turn of said first thread and the frontmost turn of said second thread both terminating adjacent to the boundary between the front and rear portions of said shank and closely adjacent to and in alignment with each other so that said first and second threads constitute continuations of each other along said shank, said first and second threads having substantially the same major diameter and corresponding to that of said threaded opening, said first and second threads having substantially the same minor diameter and corresponding to that of said threaded opening, said first and second pitches being substantially different from each other and said second pitch corresponding to that of said threaded opening, said second thread having a length along said shank that is somewhat greater than the length of said body and being arranged in engagement with said threaded opening, whereby in the initial forward driving movement of said terminal screw into its set position with respect to said body said first thread forms a corresponding threaded structure in a pilot hole provided in said body and then said second thread breaks-up the threaded structure mentioned and forms the structure of said threaded opening, and whereby in initial retrograde movement of said fastener from its set position into its partially withdrawn position said second thread rotates easily in said threaded opening and in further retrograde movement of said fastener beyond its partially withdrawn position said first thread binds in said threaded opening, thereby effectively to secure said fastener in place in said threaded opening and to establish said ready movements of said fastener between its set position and its partially withdrawn position'.

References Cited in the file of this patent UNITED STATES PATENTS 1,395,788 Anthony Nov. 1, 1921 1,487,682 Leppert Mar. 18, 1924 2,360,826 Cherry Oct. 24, 1944 2,610,390 Locke Sept. 16, 1952 2,701,870 Obszarny Feb. 8, 1955 2,779,010 Pifer Jan. 22, 1957 2,829,696 Wagner Apr. 8, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No; 3,124 408 V March 10 1964 Louis Oestereicher It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 7, line l for "shank" read first Signed and sealed this 21st day of July, 1964,

(SEAL) Attest:

ESTQN G. JOHNSON EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A SCREW FASTENER OF THE SELF-THREADING TYPE COMPRISING AN ELONGATED SHANK, AN ENLARGED HEAD TERMINATING THE REAR END OF SAID SHANK, A FIRST THREAD CARRIED BY THE FRONT PORTION OF SAID SHANK AND INCLUDING A NUMBER OF HELICAL TURNS AND HAVING A FIRST FIXED PITCH, AND A SECOND THREAD CARRIED BY THE REAR PORTION OF SAID SHANK AND INCLUDING A NUMBER OF HELICAL TURNS AND HAVING A SECOND FIXED PITCH, THE FRONTMOST TURN OF SAID FIRST THREAD TERMINATING ADJACENT TO THE FRONT END OF SAID SHANK AND THE REARMOST TURN OF SAID SECOND THREAD TERMINATING ADJACENT TO THE REAR END OF SAID SHANK, THE REARMOST TURN OF SAID FIRST THREAD AND THE FRONTMOST TURN OF SAID SECOND THREAD BOTH TERMINATING ADJACENT TO THE BOUNDARY BETWEEN THE FRONT AND REAR PORTIONS OF SAID SHANK AND CLOSELY ADJACENT TO AND IN ALIGNMENT WITH EACH OTHER SO THAT SAID FIRST AND SECOND THREADS CONSTITUTE CONTINUATIONS OF EACH OTHER ALONG SAID SHANK, SAID FIRST AND SECOND THREADS HAVING SUBSTANTIALLY THE SAME MAJOR DIAMETER AND HAVING SUBSTANTIALLY THE SAME MINOR DIAMETER AND SAID FIRST AND SECOND PITCHES BEING SUBSTANTIALLY DIFFERENT FROM EACH OTHER, THE ROOTS OF THE TURNS OF SAID FIRST THREAD HAVING A GREAT AMOUNT OF TRUNCATION AND THE ROOTS OF THE TURNS OF SAID SECOND THREAD HAVING A SMALL AMOUNT OF TRUNCATION, WHEREBY IN THE FORWARD DRIVING MOVEMENT OF SAID FASTENER INTO A SET POSITION WITH RESPECT TO AN ASSOCIATED WORKPIECE SAID FIRST THREAD FORMS A CORRESPONDING FIRST THREADED STRUCTURE IN THE WORKPIECE PILOT HOLE AND THEN SAID SECOND THREAD BREAKS-UP THE FIRST THREADED STRUCTURE MENTIONED AND FORMS A CORRESPONDING SECOND THREADED STRUCTURE IN THE WORKPIECE PILOT HOLE, AND WHEREBY IN INITIAL RETROGRADE MOVEMENT OF SAID FASTENER FROM ITS SET POSITION INTO A PARTIALLY WITHDRAWN POSITION WITH RESPECT TO THE WORKPIECE SAID SECOND THREAD ROTATES READILY IN THE SECOND THREADED STRUCTURE MENTIONED AND IN FURTHER RETROGRADE MOVEMENT OF SAID FASTENER BEYOND ITS PARTIALLY WITHDRAWN POSITION WITH RESPECT TO THE WORKPIECE SAID FIRST THREAD BINDS IN THE SECOND THREADED STRUCTURE MENTIONED, THEREBY EFFECTIVELY TO SECURE SAID FASTENER TO THE WORKPIECE AND TO ESTABLISH A LIMITED RANGE OF SUBSEQUENT READY MOVEMENTS OF SAID FASTENER BETWEEN ITS SET POSITION AND ITS PARTIALLY WITHDRAWN POSITION. 